According Quora's policy on deleting questions that you post:
After adding a question, the OP (original poster of the question) has a grace period during which he or she is permitted to delete the question; this grace period ends when a certain level of activity on the page has occurred
Expect to be able to delete a question only in a very short window of time or before anyone starts posting replies or too many people follow the question.
To delete the question:
1. Go to the question page.
2. Click "Options" under the question.
3. Click "Delete Question".
You will then be asked to give an explanation for the deletion of the question. By the grace of Quora, the question will then be deleted.